I can not figure out how to set this problem up. I know the answer is 200 mi, 220 mi.

Two different routes between two cities differ by 20 miles. Bill and Lou made the trip between the cities in exactly the same time. If one traveled the shorter route at 50 mph and the other traveled the longer route at 55 mph, how long is each route?

1 answer

shorter route --- x miles
longer route ---- x+20 miles

Since time = distance/rate
time for shorter route = x/50
time for longer route = (x+20)/55
but the times are equal, so

x/50 = (x+20)/55
55x = 50x + 1000
5x = 1000
x = 200

shorter route = 200 miles
longer route = 200+20 = 220 miles